1. Field of the Invention
The present invention generally relates to a synchronous cross-connect system among a terminal multiplexer, an add-drop multiplexer and a cross-connect system in digital transmission fields. More particularly, it relates to a synchronous cross-connect system with an integrated 2.5 Gbps input/output (hereinafter referred to as I/O) link and a ring network interworking.
2. Description of the Conventional Art
In a conventional synchronous cross-connect system, synchronous signals were only flowing in an internal switch matrix, and I/O signals were mostly typical asynchronous DS-3 signals. In recent times, STM-1 signal and STM-4 signal have been used as a synchronous I/O signal. The above prior art is described in U.S. Pat. No. 5,436,890, entitled "INTEGRATED MULTI-RATE CROSS-CONNECT SYSTEM".
In a conventional system, most I/O signals are not a transmission signal between stations (hereinafter referred to as an inter-office transmission signal) but an inter-office connection signal within a station. Accordingly, an apparatus having an optical transmission function should be additionally installed to transmit the intra-office transmission signal such as STM-16, and corresponding I/O signals should be add-dropped and connected to the cross-connect system.